Multistage cylinder

ABSTRACT

A multistage cylinder comprises at least a first-stage cylinder and a second-stage cylinder provided essentially in the piston rod of the first-stage cylinder, the first-stage and second-stage cylinders being capable of operating separately and independently of each other, whereby they can even operate in opposite directions.

United States Oraoda et a1. Sept. 9, 1975 MULTISTAGE CYLINDER 2,510,314 6/1950 Jirsa 91 167 x 2,858,802 11/1958 Parsons et a1..... 92/163 X [76] Inventors: 1 OM93 N 2933070 4/1960 Triimper et a1... 92/62 x Tokalchba-machh 3,139,004 6 1964 Haumann 92/52 x Yok h Kanagawa; Yvshimasa 3,236,620 2 1966 \Niley 92/52 x 1110, N0. 1317, Shinsaku, 3,259,027 7/1966 Phillipson ct a1. 92/52 X Takatsu-ku, Kawasaki, Kanagawa 3,285,287 11/1966 Curran 92/62 X both f J a 3,602,326 8/1971 Garrison 91/413 X F] A 23 1973 3,696,712 10/1972 Sung 92/52 22 i d: r. 1 e p FORE1GN PATENTS OR APPLICATIONS [21] APPL 353,612 328,113 1/1902 France 92/169 1,280,935 11/1961 France 92/163 [30] Foreign Application Priority Data Jan 31 J21 an M2708 Primary ExaminerMartin P. Schwadron 7 p Assistant Examiner-Abraham Hershkovitz [52] U S Cl 925}, 91/39 91/167 R Attorney, Agent, or FirmWaterS, Schwartz & Nissen 92/62;92/65;92/111;92/112;9 2/113 I; 51 161. C1. FMB 7/20 ABSTRACT [58] Fi ld 1? S ar h 92/52, 62, 66, 111 112 A multistage cylinder comprises at least a first-stage 92/113, 65, 163, 164, 169; 91/167, 35 cyiinder and a second-stage cylinder provided essentiaily in the piston rod of the first-stage cylinder, the [56] Referen Cit d first-stage and second-stage cylinders being capable of UNITED STATES PATENTS operating separately and independently of each other, 1173.358 91,!939 Ernst n X whereby they can even operate in opposite d1rect10ns. 2,397,106 3/1946 Hailcr 92/52 X 11 (3131111, 7 Drawing Figures 32 35 CONTROL L POSITiON DETEC 51GNAL GEN AIR

SOURCE PATENTED 93975 3,904,416

SHEET 1 or 5 FIG. I

CONTROL PATENTEB $5? 91975 SHEET E OF 5 MUEDOW om E nmm mop mm 200 EDMZQ UMJM m DE MULTISTAGE CYLINDER BACKGROUND OF THE INVENTION This invention relates generally to a multistage cylinder and more particularly to a multistage cylinder in which a plurality of cylinder tubes can be individually actuated independently of each other by a fluid such as an oil or air.

In multistage cylinders known heretofore, the interiors of the cylinders of all stages in each case are intercommunicative, and the cylinders of the stages are adapted to elongate and contract or retract .in sequence. Accordingly, the cylinders cannot be actuated independently, and the speed of elongating and contracting of the entire cylinder assembly is slow. Moreover, it is not possible to obtain readily any desired length of elongation or contraction.

Recently, there have been developments of devices for automatically accomplishing the operations of, for example, transporting certain articles from a specific supply position to a plurality of shelves of progressively varying heights and loading each shelf with a specific number of the articles. In the case where, in an automatic device of this character, multistage cylinders are used to constitute arm members for carrying out the operations of clutching the articles and loading them on the shelves, the loading position and heightdiffers each time an article is loaded onto a shelf. For this reason, it is necessary for each cylinder, as a whole, to assume a specific different mode of extension or contraction for each operational action.

A conventional multistage cylinder, however, cannot undergo such a complicated extension and contraction action of differing mode for each operational action, and it has not been possible to use a conventional multistage cylinder in an automatic device as described above.

On one hand, among cylinders, in general, there are servo-cylinders capable of assuming any position in extension or contraction and so-called on-off cylinders capable of assuming only two positions, i.e., an extended position and a retracted position. While a servocylinder is capable of assuming any extensioncontraction length, it requires a servo system for its operation and is therefore expensive. Another disadvantage of a servo-cylinder is that it is difficult to assembly in multiple stages. On the other hand, while the on-off cylinder is relatively inexpensive and is of a relatively simple organization, it has the drawback of not being capable of assuming any desired extension-retraction position.

SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a new and useful multistage cylinder wherein the difficulties accompnaying the conventional multistage cylinders have been overcome.

More specifically, an object of the invention is to provide a multistage cylinder in which cylinders of a'plurality of stages can operate individually and indepen dently of each other in the same or mutually opposite directions.

Another object of the invention is to provide a multistage cylinder capable of assuming any extension-retraction position through the use of a single servo-cylinder and one or more on-off cylinders.

Still another object of the invention is to provide a multistage cylinder which is highly effective when applied to apparatuses, particularly industrial robots and the like.

Further objects and features of the present invention will be apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. Us a combination of a side view in longitudinal section of one embodiment of a multistage cylinder according to the present invention and a block diagram showing one embodiment of a control system thereof;

FIGS. 2A and 2B are respectively a side view in longitudinal section and a section taken along line IIII in FIG. 2A of a second embodiment of a multistage cylinder according to the invention;

FIG. 3 is a side view in longitudinal section of a third embodiment of a multistage cylinder according to the invention;

FIG. '4 is a side elevation, with parts cut away and parts shown in longitudinal section, showing one embodiment of an automatic carrying and loading machine to which the multistage cylinder of the invention is applied;

FIG. 5 is a simplified schematic diagram showing the essential organization of a more specific and practical embodiment of the control system shown in FIG. 1 in the case where air is used for the working fluid of system; and

FIG. 6 is a simplified schematic diagram showing the essential organization of a still more specific embodiment of the control system shown in FIG. 1 in the case where an oil is used for the working fluid of the system.

DETAILED DESCRIPTION A first embodiment of a multistage cylinder according to the present invention will now be described with reference to FIG. 1.

To the inner and outer ends of a first cylinder tube 11 of the multistage cylinder 10 according to the invention, there are respectively fixed a head cover 12 and a first rod cover 13, gas-tight packings being suitably provided between these covers and the cylinder tube. The head cover 12 is provided therethrough with a supply and discharge pipe 14 for inflow and outflow of pressurized fluid, while the rod cover 13 is similarly provided therethrough with a supply-discharge pipe 15. Examples of the above mentioned pressurized fluid suitable for use according the invention are pressurized air, oil, and other gases and liquids. In the instant embodiment illustrated in FIG. 1, pressurized air is used.

Within the first cylinder tube 11, there is slidably fitted a first piston 16, to which is fixed the inner end of a first piston rod 17 of hollow cylindrical shape, which is slidably fitted in and through a hole 18 formed coaxially in the rod cover 13, a gas-tight packing being interposed between this piston rod and the rim of the hole. The above mentioned cylinder tube 11, head cover 12, rod cover 13, piston 16, piston rod 17, and supply and discharge pipes 14 and 15 constitute a first-stage cylinder l9.

Within the first piston rod 17, there is coaxially disposed a second cylinder tube fixed at the inner end thereof to the first piston 16. The other ends of the first piston rod and the second cylinder tube 20 are secured to a second rod cover 21 with gas-tight packings interposed therebetween. The outer diameter of the second sylinder tube 20 is less than the inner diameter of the first piston rod 17, and a cylindrical space 22 is formed between the first piston rod 17 and the second cylinder tube 20. Near the outer end (the right end as viewed in FIG. 1) of the first piston rod 17, there is provided a supply-discharge pipe 23 for pressurized fluid communicating with the space 22. Near the inner end of the second cylinder tube 20 fixed to the first piston 16, a plurality of holes 24 aare formed in the cylindrical wall of the cylinder tube 20. These holes 24 also communicate with the space 22.

Within the second cylinder tube 20, there is slidably fitted a second piston 25. A second piston rod 26 is fixed at its inner end to this second piston and is slidably fitted in and through a hole 27 formed in the center of the second rod cover 21 a suitable gas-tight packing being interposed therebetween. The other outer end of this second piston rod 26 is coupled to a part to be actuated by the multistage cylinder. The second rod cover 21 is provided with a fluid supply-discharge pipe 28. The second piston 25 has leg parts 25:: projecting inward or toward the first piston 16 and acting as stop means. When the piston 26 is in its innermost position relative to the piston 16, the inner ends of these leg parts 251: are abutting against the outer side of the piston 16, whereby the piston is stopped and a cham ber communicating through the holes 24 with the space 22 is formed between the first and second pistons l6 and 25.

The above described second cylinder tube 20, the second piston 25, the second piston rod 26, the outer (right-hand) wall surface of the first piston 16, the second rod cover 21, and the supply-discharge pipes 23 and 28 constitute a second-stage cylinder 29.

The aforementioned supply-discharge pipe 14 communicates with a space defined and enclosed by the head cover 12, the first cylinder tube 11, and the first piston 16. The supply-discharge pipe 115 communicates with a space defined and enclosed by the first piston 16, the first cylinder tube 11, the first piston rod 17, and the first rod cover 13. The supply-discharge pipe 23 communicates with a space defined and enclosed by the first and second pistons 16 and 25 and the second cylinder tube 20. Furthermore, the supply-discharge pipe 28 communicates with a space defined and enclosed by the second piston 25, the second cylinder tube 20, and the second rod cover 21.

The multistage (two-stage) cylinder of the above described construction according to the invention operates as follows. When the working fluid (air) under pressure is supplied through the supply-discharge pipe 14 into the chamber between the head cover 12 and the first piston 16, the piston 16 and the first piston rod 17 are forced outward or toward the right as viewed in FIG. 1. When pressurized air is supplied through the supply-discharge pipe 23, it passes through the space 22 and holes 24 into the chamber 30, whereby the secondpiston 25 and the second piston rod 26 are forced outward. On the other hand, when pressurized air is supplied through the supply-discharge pipe 28, the second piston 25 and rod 26 are forced inward. The supply or discharge of pressurized air through the supplydischarge pipe 14 or 15 and that through the supplydischarge pipe 23 or 28 can be carried out separately and independently of each other. Accordingly, the first and second pistons 16 and 25 can be operated to slide independently of each other in the same direction or in mutually opposite directions.

The supply and discharge of pressurized air through these supply-discharge pipes 14, 15, 23, and 28 are controlled by a control system of the following organization and operation. In this control system, a program for a prescribed operation of the multistage cylinder is previously stored, and in accordance with this program, a signal is generated by a signal generator 31 and sent to a controller 32 and changeover valve 33. The controller 32 and the changeover valve 33 are supplied with pressurezed air from an air source 34.

The changeover valve 33 operates in accordance with the signal from the signal generator 31 to changeover the destination of delivery of pressurized air from the air source 34, thereby to supply the air to either the aforementioned supply-discharge pipe 23 or 28. When the pressurized air is supplied to the pipe 23, the second piston 25 is forced to slide outward to the outward end of its stroke, while when the pressurized air is supplied to the pipe 28, the piston 25 is forced to slide inward to the inward end of its stroke. Thus, the piston 25 changes its position between only the two positions, namely, those of the outer end and the inner end of its stroke, and the second-stage cylinder 29 operates on an onoff cylinder.

On the other hand, as the first piston 16 of the firststage cylinder 19 undergoes sliding movement, its position at each instant is detected by a position detector 35 as being interrelated to the varying position of the second rod cover 21, whereupon the position detector 35 generages a detection output, which is supplied to the controller 32. The controller 32 thereupon operates in response to this detection output in conjunction with a signal from the signal generator 31 to control the supply of pressurized air from the air source 34 to the supply-discharge pipes 14 and 15. Therefore, depending on the state of air supply to the supply-discharge pipes 14 and 15, the first pistion 16 can be moved to any desired position, and the first-stage cylinder 19 operates as a servo-cylinder.

Then, since this first-stage cylinder 19 is a servocylinder, the second piston rod 26 of the second cylinder 10 can always be caused to assume any variable position within its total stroke from the most contracted or retracted state wherein the first and second pistons 16 and 25 are at their innermost positions to the most extended state wherein the pistons 16 and 25 are at their outermost positions even though the second-stage cylinder 29 is an on-off cylinder. The degree of accuracy of this variable position in this operation is determined by the accuracy of the first-stage servo-cylinder 19 and is high.

When the piston 25 of the second-stage on-off cylinder 29 changes its position to the inner end of its stroke, and the legs 25a of the piston 25 abut against the outer wall surface of the first piston 16, the piston 16 is subjected to the abutment impact force of the piston 25, but the air in the chamber formed between the first piston 16 and the head cover 12 acts as an air spring to absorb effectively the above mentioned impact force. Accordingly, there is no necessity whatsoever of providing a cushioning mechanism for this second-stage cylinder 29.

In the embodiment described above, the cylinder is made up of two stages, but it will be apparent, of course, a third-stage and succeeding on-off cylinders can be adeed to the second-stage cylinder 29 thereby to provide a multistage cylinder of three or more stages. In such a case, also, any desired position can always be obtained by using only a single servo-cylinder and an on-off cylinders for the other cylinders. It should be required that the stroke of the rod of the servo-cylinder is at least equal to or greater than the stroke of the rod of the on-off cylinder.

Since the first-stage and second-stage cylinders 19 and 29 are adapted to operate separately, as mentioned hereinabove, it is not necessary in all case to construct them coaxially in a strict sense, an eccentric construction also being possible. Accordingly, a centering step in the assembly or fabrication of each cylinder is not necessary, whereby production of the cylinder is facilitated.

Furthermore, while pressurized air is used as the driving fluid in the above described embodiment, the invention is not so limited, another fluid such as oil also being usable.

A second embodiment of the multistage cylinder according to this invention will now be described with reference to FIG. 2A and FIG. 2B. In these figures, parts which are the same as or are equivalent to those shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will not be repeated.

The multistage cylinder shown and generally designated by reference numeral 40 has a first-stage cylinder 41 comprising a cylinder tube 11, a head cover 12, a piston 16, a piston rod 43, a rod cover 44, and supplydischarge pipes 14 and provided respectively in the head cover 12 and the rod cover 44.

The piston rod 43 of the first-stage cylinder 41 serves doubly as the cylinder tube of a second-stage cylinder 42. The inner end of a supplydischarge pipe 45 is secured to the piston rod and cylinder tube 43 near its inner end fixed to the piston 16, the interior of this pipe 45 being communicative via a hole in the wall of the tube 43 with the interior thereof. This supply-discharge pipe 45, except for its inner end, is parallel to the axis of the multistage cylinder 40 and passes through the rod cover 44, being guided in sliding movement relative thereto by a guide 46. The second-stage cylinder 42 comprises the cylinder tube 43, a second pistion 25, a second piston rod 26, the outer (right-hand) wall surface of the piston 16, a second rod cover 47, the supply-discharge pipe 45, and a supply-discharge pipe 28 connected to and passing through the rod cover 47.

The supply-discharge pipe 14 is communicatively connected to a space defined by the head cover 12, cylinder tube 11, and piston 16, while the supplydischarge pipe 15 is communicatively connected to a space defined by the piston 16, cylinder tube 11, piston rod 43, and rod cover 44. The supply-discharge pipe 45 is communicatively connected to a space defined by the pistons 16 and and the cylinder tube 43, while the supply-discharge pipe 28 is communicatively connected to a space defined by the piston 25, cylinder tube 43, and rod cover 47.

The piston 16 is actuated in sliding movement by pressurized air supplied and discharged through the supply-discharge pipes 14 and 15, while the piston 25 is similarly actuated by pressurized air supplied and discharged through the supply-discharge pipes 45 and 28. The possibility of mutually independent operations of the pistons 16 and 25 is the same as that in the preceding first embodiment, and for their control, the control system illustrated in FIG. 1 can be applied.

In the instant embodiment, since the supplydischarge pipe 45 communicating with the cylinder tube 43 extends through the rod cover 44, it functions to prevent rotation of the piston rod and cylinder tube 43 relative to the other parts.

A third embodiment of a multistage cylinder according to the present invention will now be described in conjunction with FIG. 3.

This multistage cylinder 50 has a first-stage cylinder 51 comprising a cylinder tube 52, a head cover 53, a piston 54, a piston rod 55, a rod cover 56, and supplydischarge pipes 57 and 58 connected to the cylinder tube 52 respectively near the inner and outer ends thereof. A supply-discharge pipe 59 is passed through and fixed to the center of the piston 54 and extends out through a center hole 60 in the head cover 53, being fitted slidably but in a gastight manner in this center hole 60..

The piston rod 55 serves doubly as a cylinder tube of a second-stage cylinder 61 and is provided at its outer end with a rod cover 62 fixed thereto in a gas-tight manner. This cylinder tube 55 is provided near its outer end with a supply-discharge pipe 63. The second-stage cylinder 61 comprises the cylinder tube 55, the piston 54 serving doubly as a head cover, the rod cover 62, a piston 25 slidably fitted within the cylinder tube 55, a piston rod 26 fixed at its inner end to the piston 25 and extending out through the center of the rod cover 62, and the supply-discharge pipes 59 and 63.

The above mentioned supply-discharge pipe 57 is communicatively connected to a space defined by the head cover 53, the cylinder tube 52, and the inner (lefthand) wall surface of the piston 54, while the supplydischarge pipe 58 is communicative with a space defined by the piston 54, the cylinder tube 52, the piston rod 55, and the rod cover 56. The supply-discharge pipe 59 is communicative with a space defined by the piston 54, the cylinder tube 55, and the piston 25. The supply-discharge pipe 63 is communicative with a space defined by the cylinder tube 55, the piston 25, and the rod cover 62 the piston 25 has leg parts 25b acting as the stop means.

The piston 54 of the first-stage cylinder 51 is actuated in sliding movement by pressurized air supplied and discharged through the supply-discharge pipes 57 and 58, while the piston 25 of the second-stage cylinder 61 is similarly actuated by pressurized air supplied and discharge through the supplydischarge pipes 59 and 63. The possibility of mutually independent operations of the pistons 54 and 25 is the same as that in the preceding embodiments, and for their control, also, the control system shown in FIG. 1 can be applied.

Next, the multistage cylinder according to the invention will be described with respect to one embodiment of its application to a robot for industrial use, with reference to FIG. 4.

FIG. 4 illustrates one embodiment of a robot for industrial use for performing the operation of convey ing and loading specific articles, which have been successively supplied to a specific supply position, in prescribed numbers successively to and onto shelves of progressively varying height.

A hollow stationary column 71 is fixedly held in upright position by a support structure 72 on a floor surface 87. At the upper and lower ends of the stationary column 71, there are respectively provided bearing means rotatably supporting the proximal end parts of upper and lower arms 73 and 74, respectively. These arms 73 and 74 are respectively fixed to the upper and lower ends of a rotatable shaft 76 disposed coaxially within the stationary column 71. The distal ends of the arms 73 and 74 are joined by a tie rod 75 fixed at its upper and lower ends thereto and disposed parallelly to the stationary column 71. A pinion 77 is provided on the proximal part of the lower arm 74 and is meshed with and driven by a rack 78 driven by motive power means (not shown).

A slider 79 is slidably fitted around the stationary column 71 at approximately its middle part and can thereby slide vertically relative to the column 71. This slider 79 is pin-connected to the outer end of a piston rod 81 of a cylinder 80 for up-and-down movement pin-connected at its head cover end to a part of the support structure 72. A rotor 82 is fitted on the stationary column 71 in a manner permitting vertical sliding and rotational movements and is resting rotatably on the slider 79. This rotor 82 is actuatable through an arm 83 to rotate unitarily with the rod 75.

The rotor 82 supports a multistage cylinder 84 according to this invention, as exemplified by any of the above described cylinders 10, 40, and 50, the multistage cylinder 84 being mounted at its head-cover end on the rotor 82. A grasping device 86 for grasping the aforementioned specific articles is mounted on the outer end of the piston rod 85 of the second-stage cylinder of this multistage cylinder 84.

In the operation of the robot machine of the above described structure, the sliding of the rack 78 causes the pinion 77, and therefore the arm 74, to rotate. Consequently, the shaft 76, arm 73, rod 75, rotor 82, and multistage cylinder 84 all rotate unitarily with the arm 74 about the axis of the shaft 76, whereby the grasping device 86 swings in a horizontal plane. Operation of the cylinder 80 causes its pistion rod 81 to move out or inv thereby to actuate the slider 79, rotor 82, and multistage cylinder 84 in upward or downward movement, whereby the grasping device 86 is moved vertically up or down.

Together with or separately from the above described rotation and vertical movement, the grasping device 86 can be caused by the operation of the multistage cylinder 84 to move horizontally toward or away from the stationary column 71. By causing the grasping device 86 to carry out the operations of grasping and releasing the articles to be handled together with the combination of the above described rotation, vertical movement, and horizontal displacement, it is possible to cause the robot machine 70 to perform readily complicated operations such as loading articles at a specific height position of a prescribed number thereof on each of a plurality of shelves of successively varying height.

Specific embodiments of the cylinder control system indicated by simplified block diagram in FIG. 1 will nowbe described in detail with reference to FIGS. and 6.

The embodiment illustrated in FIG. 5 is applied to the control of multistage cylinder actuted by pressurized air as the driving fluid. In FIG. 5, parts which are the same or equivalent to those in FIG. 1 are designated by like reference numerals, but detailed description thereof will not be repeated.

Pressurized air is supplied by a pressurized air source 90 by way of a pressure-reducing valve 91 to a manifold 92, where the pressurized air is branched and supplied through pipes 93, 94, 95, and 96. The pipe 93 is communicatively connected to a nozzle and the aforementioned supply-discharge pipe 14, and the pipe 94 is communicatively connected to a nozzle in opposed relation to the nozzle 97 and to the aforementioned supply-discharge pipe 15.

Between the nozzles 97 and 98, there is interposed a shield plate 99 pivotally supported at one end thereof. This shield plate is pulled toward one side (toward the nozzle 97) by a counter spring 100 and toward the opposite side by a spring 102 provided on a position detection member 101 fixed to the rod cover 21, which is fixed to the piston rod 17 of the first stage cylinder The pressurized air in the pipe 95 is supplied through a pressure-reducing valve 103 to an electropneumatic converter 104 where it is converted into a pneumatic signal of a pressure in accordance with an electrical signal from the signal generator 31. This pneumatic signal is supplied by way of a pipe 105 to a diaphragm chamber 106 to determine a displaced position of the shield plate 99. By the displacement of the shield plate 99, the air discharges from the nozzles 97 and 98 are controlled, whereby the manner in which air from the pipes 93 and 94 are supplied to the supply-discharge pipes 14 and 15 and the manner in which air is discharged from the pipes 15 and 15 are controlled, and the first-stage cylinder 19 shown in FIG. 1 is operated as a servocylinder.

On the other hand, the pressurized air in the pipe line 96 is supplied to a changeover valve 33. This changeover valve 33 comprises an electromagnetic changeover valve, for example, wherein solenoids 33a and 33b operate in accordance with an electrical signal from the signal generator 31 to carry out valve changeover. As a result of the changeover operation of the valve 33, the pressurized air is suppled to the supply-discharge pipe 23 or 28. At this time, the supply-discharge pipe which is not supplied with pressurized air is communicative by way of the changeover valve 33 with the atmosphere. Therefore, the second-stage cylinder is activated only by the existence or absence of the supply of pressurized air and operates as an on-off cylinder.

FIG. 6 illustrates an embodiment of a control system in the case where an oil is used as the driving fluid. Pipes 111 and 112 from an oil pressure source are connected by way of a servovalve 113 to the supplydischarbe pipe 14 or 15. On the other hand, position detection of the piston rod 17 of the first-stage cylinder 19 is carried out by a position detector 114 comprising a differential transformer in accordance with the displacement of a position detecting member 101 fixed to the rod cover 21 which is fixed in turn to the piston rod 17 of the first-stage cylinder 19.

A servo-amplifier 115 receives an electrical signal from the signal generator and the detection output of the position detector 114 to produce a resulting output whereby the servovalve 113 is controlled, and supplying and discharging of pressurized oil through the supply-discharge pipes 14 and 15 are so carried out that the piston rod 17 of the first-stage cylinder 19 moves accurately to the position designated by the signal from the signal generator 31. Accordingly, the first-stage cylinder operates as a servo-cylinder.

On one hand, pipes 116 and 117 are connected between the oil pressure source 110 and the changeover valve 33. The changeover valve 33 is caused to carry out changeover switching of connections of supplydischarge pipes 23 and 28 and pipes 116 and 117 by solenoids 33a and 33b activated by a signal from the signal generator 31. Accordingly, the second-stage cylinder is operated only in accordance with whether or not pressurized oil is being supplied thereto and operates as an on-off cylinder.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope and spirit of the invention.

What we claim is:

l. A multistage cylinder having at least a first-stage cylinder and a second-stage cylinder, in which: the first-stage cylinder comprises a first cylinder tube,

a head cover fixed to one end of the first cylinder tube,

a first piston of disc shape slidably disposed within the first cylinder tube,

a first piston rod of tubular shape fixed at one end thereof to the first piston,

a first rod cover fixed to the other end of the first cylinder tube and having a hole through which the first piston rod slidably extends,

a first supply-discharge pipe constituting a communicative passage through the head cover from outside of the multistage cylinder to a first space defined within the first cylinder tube by the head cover and the first piston and functioning to supply and discharge a fluid to and from said first space, and

a second supply-discharge pipe constituting a communicative passage through the first rod cover from outside of the multistage cylinder to a second space defined within the first cylinder tube by the first piston and the first rod cover and functioning to supply and discharge a fluid to and from said second space,

the supply and discharge of the fluid through the first and second supply-discharge pipes being carried out in a mutually interrelated manner; and

the second-stage cylinder comprises a second cylinder tube disposed within the first piston rod with a specific clearance space therebetween and fixed at one end thereof to the first piston,

a second piston of disc shape slidably disposed within the second cylinder tube,

said second cylinder tube being provided with an opening near the part thereof fixed to the first piston, said opening for communicating a third space defined within the second cylinder tube by the first piston and the second piston with the specific clearance space,

a clearance member for maintaining a clearance between the first and second pistons so that the second piston does not close the opening of the second cylinder tube when the second piston is slid to the closest position to the first piston.

a second piston rod fixed at one end thereof to the second piston,

a second rod cover fixed to the other ends of the first piston rod and the second cylinder tube and having a hole through which the second piston rod slidably extends,

a third supply-discharge pipe constituting a communicativc passage to the specific clearance space from outside of the multistage cylinder and functioning to supply and discharge a fluid to and from said third space through the specific clearance space, and

a fourth supply-discharge pipe constituting a communicative passage through the second rod cover from outside of the multistage cylinder to a fourth space defined within the second cylinder tube by the second piston and the second rod cover and functioning to supply and discharge a fluid to and from said fourth space,

the supply and discharge of the fluid through the third and fourth supply-discharge pipes being carried out in a mutually interrelated manner and in an individual manner with respect to the first and second supply-discharge pipes. l =I 

1. A MULTISTAGE CYLINDER HAVING AT LEAST A FIRST-STAGE CYLINDER AND A SECOND-STAGE CYLINDER, IN WHICH: THE FIRST-STAGE CYLINDER COMPRISES A FIRST CYLINDER TUBE, A HEAD COVER FIXED TO ONE END OF THE FIRST CYLINDER TUBE A FIRST PISTION OF DISC SHAPE SLIDABLY DISPOSED WITHIN THE FIRST CYLINDER TUBE, A FIRST PISTION ROD OF TUBULAR SHAPE FIXED AT ONE END THEREOF TO THE FIRST PISTON, A FIRST ROD COVER FIXED TO THE OTHER END OF THE FIRST CYLINDER TUBE AND HAVING A HOLE THROUGH WHICH THE FIRST PISTON ROD SLIDABLY EXTENDS, A FIRST SUPPLY-DISCHARGED PIPE CONSTIUTING A COMMUNICATIVE PASSAGE THROUGH THE HEAD COVER FROM OUTSIDE OF THE MULTISTAGE CYLINDER TO A FIRST SPACE DEFINED WITHIN THE FIRST CYLIMDER TUBE BY THE HEAD COVER AND THE FIRST PISTON AND FUNCTIONING TO SUPPLY AND DISCHARGE A FLUID TO AND FROM SAID FIRST SPACE, AND A SECOND SUPPLY-DISCHARGE PIPE CONSTITUTING A COMMUNICATIVE PASSAGE THROUGH THE FIRST ROD COVER FROM OUTSIDE OF THE MULTISATAGE CYLINDER TO A SECOND SPACE DEFINED WITHIN THE FIRST CYLINDER TUBE BY THE FIRST PISTON AND THE FIRST ROD COVER AND FUNCTIONING TO SUPPLY AND DISCHARGE A FLUID TO AND FROM SAID SECOND SPACE, THE SUPPLY AND DISCHARGE OF THE FLUID THROUGH THE FIRST AND SECOND SUPPLY-DISCHARGE PIPES BEING CARRIED OUT IN A MUTUALLY INTERRELATED MANNER: AND THE SECOND-STAGE CYLINDER COMPRISES A SECOND CYLINDER TUBE DISPOSED WITHIN THE FIRST PISTON ROD WITH A SPECIFIC CLEARANCE SPACE THEREBETWEEN AND FIXED AT ONE END THEREOF TO THE FIRST PISTON, A SECOND PISTON OF DISC SHAPE SLIDABLY DISPOSED WITHIN THE SECOND CYLINDER TUBE, SAID SECOND CYLINDER TUBE BEING PROVIDED WITH AN OPENING NEAR THE PART THEREOF FIXED TO THE FIRST PISTON, SAID OPENING FOR COMMUNICATING A THIRD SPACE DEFINED WITHIN THE SECOND CYLINDER TUBE BY THE FIRST PISTON AND THE SECOND PISTON WITH THE SPECIFIC CLEARNCE SPACE, 